1. Field of the Invention
The present invention relates to heaters that heat a print head of a hot melt ink jet printer.
2. Description of Related Art
A hot melt ink Jet printer (hereinafter referred to as "a printer") includes a print head mounted on a carriage. The print head includes a heating tank, an ink tank, a plurality of nozzle heads, and heaters for heating these components. A hot melt ink (hereinafter referred to as an "ink") is in its solid state at a normal temperature and changes to its liquid state when heated. Solid ink supplied to the heating tank is heated, melted, and supplied to the ink tank and further to the nozzle head. The ink in the ink tank and the nozzle head is maintained in its liquid state. Each of the nozzle heads includes a piezoelectric member forming an ink channel. When applied with a voltage, the piezoelectric member is deformed, thereby changing the internal pressure of the ink channel. As a result, ink in the ink channel is ejected as an ink droplet toward a printing medium.
When the printer is powered OFF after printing operation, ink remaining in the ink tank and the nozzle heads is cooled off and solidified while trapping air bubbles. Therefore, before starting the printing operation next time, a preparatory operation is required. That is, the solidified ink in the ink tank and the nozzle heads is melted. Also, the air bubbles are removed from the ink.
As shown in a graph in FIG. 1, both a heater and a nozzle head, that is, ink in the nozzle head, are at a normal temperature when a printer is powered ON. The heater starts generating heat and keeps increasing its temperature, and then, is leveled off at a predetermined temperature, which is slightly higher than an ink maintained temperature. Also, the heater heats up the ink to melt at the same time. However, the temperature increasing rate of the ink is lower than that of the heater. Then, the melted ink is maintained at the ink maintained temperature, for example, 120.degree. C., in the liquid state. Then, the air bubbles are removed from the ink by a purging operation. In this way, the printer is set ready for the printing operation.
However, it may take a long time for the heater to heat up ink to the ink maintained temperature. Also, ink in different locations within the print head cannot increase its temperature at a uniform speed. For example, the nozzle head takes a longer time duration to reach the predetermined temperature than the ink tank.